One of the representative examples of the conventional method for the production of calcium phosphate porous material comprises adding and mixing an aqueous solution of a deflocculant (foaming stabilizer) with micronized calcium phosphate, adding a surfactant (foaming agent) into the resulting mixture to prepare porous fluid having communicated fine pores, subjecting to the porous fluid to a drying treatment to give porous forming material with calcium phosphate structure, calcining the resulting forming material by constantly heating it up to a temperature of 1,000° C. or more at a temperature-rising rate of about 300° C. per hour by means of an electric furnace and the like so as to decompose and vanish said deflocculant and surfactant while sintering it as ceramic (Patent Document 1). This method is depicted in FIG. 1.
Another example of the conventional method for the production of calcium phosphate porous material comprises a step of crushing granule premix consisting of wax binder and micronized calcium phosphate ceramic into granule material with a predetermined diameter, a step of mixing and dispersing said granule material in aqueous foaming slurry consisting of micronized calcium phosphate ceramic, and a step of casting the resulting mixture into a mold with a predetermined shape and a step of drying and calcining the mixture to give prosthetic bone material (Patent Document 2).
Micronized calcium phosphate are known hydroxyapatite and β-tricalcium phosphate. An artificial bone made of hydroxyapatite will bind to bone and have a sufficient initial strength, but is not absorbent. On the other hand, an artificial bone made of β-tricalcium phosphate is absorbent so that it can substitute autologous bone. A method for the mechanochemical production of such micronized calcium phosphate is disclosed, for example, in Patent Documents 3 and 4, and Non-Patent Document 1.
According to the conventional heating and calcining disclosed in the above documents, additives such as the deflocculant, surfactant and/or binders could not be sufficiently decomposed and vanished. Therefore, polycyclic aromatic hydrocarbons would be generated from carbon atoms contained in said additives and remain in such an amount as would affect a living body.
The term “polycyclic aromatic hydrocarbons” is a generic one that means compounds generated due to incomplete combustion during burning of material, some of which are known as showing strong cancer-causing or promoting properties.
In the prior method disclosed in Patent Documents 1 and 2, the calcining or sintering step was performed by heating up to a predetermined temperature (for example, at 1,000˜1,300° C.) with a constant temperature-rising rate (for example, 300° C. per hour) and keeping at the predetermined temperature for a certain period of time, or just by heating at a predetermined temperature for a certain period of time. Nothing is described in the above prior art with respect to an amount of the remaining polycyclic aromatic hydrocarbons in the produced calcium phosphate porous material.                [Patent Document 1] Japanese Patent No. 2597355        [Patent Document 2] Japanese Patent Laid-Open Application No. 1993-237178        [Patent Document 3] Japanese Patent No. 3262233        [Patent Document 4] Japanese Patent Publication No. 1991-69844        [Non-Patent Document 1] Motohiro TORIYAMA and Sukezo KAWAMURA, Synthesis of β-Tricalcium Phosphate by use of Wet Milling, Yogyo-Kyokai-shi, 94, 78-82, 1986        